This invention relates to the hydrologic control of lakes and ponds and more particularly to an apparatus and method for automatically controlled withdrawal of bottom water for controlling the growth of aquatic weeds and algae.
Lakes, ponds and other impoundments are frequently polluted by an excess growth of aquatic macrophytes, algae, and other microorganisms which create unacceptable water quality conditions for recreation, water supply, and wild life habitat during the growing season. As surface water becomes warm during the spring, the bottom water of a water body, such as a lake, becomes isolated from atmospheric gas exchange due to the differences in water density at different water temperatures. The desnity layers formed in the lake therefore result in different water quality between the surface water and the bottom water.
As organic materials decompose at the bottom of the lake, oxygen is consumed and carbon dioxide and nutrients are generated and released. The decomposition process results in the release of large amounts of phosphorus, nitrogen, carbon dioxide and other substances from the nutrient-rich sediments at the bottom of the lake and, during the growing season, the nutrients generated from the lake bottom contribute to the excessive growth of macrophytes and algae and the attendant unacceptable water conditions.
It is an object of the present invention to provide an apparatus and method for controlling aquatic macrophyte and algae growth by altering the outflow configuration of the water body for controlled discharge of bottom water as well as surface water.
Another object of the invention is to provide an apparatus and method for removing dense cool oxygen-deficient nutrient-rich bottom water from a water body at a rate which automatically adjusts to varying hydrologic conditions.
A further object of the invention is to provide an improved hydrologic discharge control assembly for the automatic withdrawal of bottom water without the need for pumping, siphoning, frequent adjustments, or large fluctuations in water level.
Yet another object of the invention is to provide a hydrologic discharge control assembly which achieves automatic bottom water withdrawal, adjustable surface-bottom water outflow ratios, and adequate flood storage while minimizing water body level fluctuations.
Other objects will be in part obvious and in part pointed out in detail hereinafter.